It is known, e.g. from U.S. Pat. No. 3,344,324 to produce a field-effect transistor (FET) of this description from a substrate of a first conductivity type (P) integrally formed with a layer of the opposite conductivity type (N) supporting source and drain electrodes which are separated by a groove or trench, the latter terminating short of a P/N junction existing between the layer and the substrate so as to leave a narrow N-type channel whose conductivity can be controlled by a gate electrode deposited on the opposite substrate surface. The main electrodes are in contact with a more highly conductive region of the N-type layer obtained by the diffusion of impurities into that layer from the exposed surface thereof. This local enrichment of a semiconductive layer with charge carriers by a diffusion technique, however, is very difficult to carry out with certain semiconductor materials, such as gallium arsenide (AsGa).
Another problem arising with such FETs, especially those designed to operate under high power at elevated frequencies, is the need for preventing discharges ("flashing") between the source and drain electrodes across the intervening trench. It is also important to avoid the flow of leakage currents across the exposed surface areas of the layer which bound the semiconductive body.